Propofol (2,6 diisopropylphenol) is a hydrophobic, water-insoluble oil which is widely used as an anesthetic agent via IV administration. Propofol is generally incorporated in a vegetable oil emulsion to enable intravenous administration.
Sterile pharmaceutical compositions of propofol and their use in inducing anesthesia are generally described in U.S. Pat. Nos. 4,056,635; 4,452,817 and 4,798,846, all to Glen and James. The propofol/soybean oil emulsion has gained widespread use for induction and/or maintenance of anesthesia, for maintenance of monitored anesthesia care and for sedation in the Intensive Care Unit (ICU). It is advantageous in that it possesses both a rapid onset anesthesia and a short recovery time.
One problem associated with the compositions described in the before mentioned patents is the risk of bacterial contamination primarily due to the high soybean oil content, and lack of antimicrobial preservatives.
It has been shown that the propofol emulsion formulated without preservatives will grow bacteria. The oil content, combined with a lack of antimicrobial additives, present a risk of bacterial contamination (Arduino et al., 1991, Sosis & Braverman, 1993; PDR, 1995).
To address the problem of bacterial contamination of propofol emulsions, additional formulations of propofol have been developed. One such formulation, is described in U.S. Pat. No. 5,731,356. It is believed that the product described in that patent is commercially marketed under the tradename DIPRIVAN and comprises a sterile, pyrogen-free oil-in-water emulsion containing 1% (w/v) propofol in 10% (w/v) soybean oil dispersed in water and stabilized by 1.2% (w/v) lecithin phospholipidis and includes a commonly used preservative, EDTA to provide a claimed benefit of less than one log increase in growth of certain gram-positive and gram-negative bacteria over a twenty-four period. Such a formulation, however, requires the administration of EDTA which is a chelating agent that removes cations such as calcium and magnesium. Removal thereof can be dangerous when administered to patients with low calcium or magnesium levels, or who have compromised control systems for those minerals.
A second formulation, described in U.S. Pat. No. 5,637,625, is an oil-free formulation in which, in one described form, the propofol is in a 6.8% wt/wt concentration and dispersed in water as micro-droplets with a diameter generally less than 1 micron, having a phospholipid or monoglyceride outer covering. However, it appears that upon administration this formulation may increase site irritation to an unacceptable level.
The problems described above are substantially reduced if not eliminated by an improved propofol formulation provided in accordance with the present invention.
Propofol emulsions of the present invention do not support the growth of bacteria, and in fact exhibit bacteriostatic properties. An important feature of the present invention is the formulation of a propofol emulsion for intravenous administration with a reduced risk of bacterial growth after site contamination which may occur in a medical care giving setting.
The preferred embodiment of the present invention provides a propofol formulation, preferably an emulsion, having antimicrobial properties without the use of antimicrobial additives and with any additives preferably limited to those generally required to prepare an oil-in-water emulsion formulation.